The present invention concerns compact fans comprising a drive motor, a fan wheel coaxial with the drive motor, and a housing surrounding the fan wheel.
For reasons of economy, fans and blowers of this type are typically provided with drive motors of the simplest possible construction having a concentric stator winding, with sizable copper rings usually being provided on the pole legs of the stator core to serve as shading rings. When powering fans and blowers, the most common of such motors are single-phase induction motors operating asynchronously--i.e., with slip--and having a short-circuited squirrel-cage rotor winding.
Shaded-pole motors of the type normally used to power small fans and blowers are very economical to produce, but have electrical and ecological disadvantages. They exhibit a fairly low efficiency--i.e., consume power somewhat wastefully--and furthermore produce a considerable amount of noise during operation due to the magnetic asymmetry of the motor design.